Inherently tacky pressure sensitive adhesive microspheres are known in the art to be useful in repositionable pressure sensitive adhesive applications and there are numerous references discussing the preparation and/or use of inherently tacky, elastomeric polymeric microspheres. Pressure sensitive adhesive microspheres may be solid or hollow and are generally crosslinked to an extent such that the particulate nature of the adhesive is maintained throughout processing and use. Typically, pressure sensitive adhesive microspheres are prepared via suspension polymerization of one or more free radically polymerizable monomers in the presence of surfactants and/or suspension stabilizers. Choice of surfactants and/or suspension stabilizers and their specific combinations with specific monomers can determine suspension stability, desired particle morphology, performance characteristics, and the like.
Various copolymerizable monomeric components have been added to the free radically polymerizable monomers, suspension stabilizers and/or surfactants to modify the adhesive properties of these suspension polymerized microspheres. For example, nitrogen-containing polar monomers have been added to acid-free acrylate suspension polymerization mixtures to form adhesive microspheres containing multiple internal voids. Polar comonomers having no dissociable protons or low levels of dissociable protons, when used along with particular surfactant and polymeric stabilizer combinations, can be added to suspension polymerizable formulations to yield adhesive microspheres having enhanced adhesive properties while maintaining their repositionable and self cleaning qualities against a variety of surfaces.
Copolymerizable or otherwise incorporated oligomeric and polymeric additives have also been employed in suspension polymerized adhesive microspheres to alter microsphere adhesive properties and other performance characteristics. Hydrophilic oligomers and polymers have been included in suspension polymerizable adhesive microsphere formulations to provide improved microsphere stability and, in some formulations, water dispersibility. Water insoluble polymeric components have also been incorporated into adhesive microspheres by suspension polymerization of alkyl(meth)acrylate and other comonomers in the presence of such polymeric components. This method of incorporation allows for the inclusion of water insoluble polymer components into adhesive microspheres that could not typically be incorporated under standard free radical suspension polymerization conditions. Another advantage of this water insoluble polymer incorporation is to modify the physical and adhesive properties of the microspheres. Finally, crystalline polymers or crystallizable monomers have also been added during suspension polymerization to provide adhesive microspheres having thermally controllable shape memory.
Drugs and other therapeutically active agents have been administered transdermally or percutaneously using a variety of methods and devices. One known method is to incorporate the drug into a continuous adhesive matrix, either alone or in combination with one or more excipients that enhance the delivery of drug across the skin. Examples of such systems are found, for example in Nelson et al., U.S. Pat. No. 5,223,261 and Peterson, U.S. Pat. No. 5,494,680.
There have been some attempts in the prior art to develop transdernal drug delivery systems that use pressure sensitive adhesive particles in place of a continuous adhesive matrix. For example, JP 58-12255 describes an adhesive tape or sheet made up of acrylic polymer particles that contain a drug such as a steroid. EP 793,972 describes a transdermal drug delivery device that contains finely pulverized acrylate adhesive particles in combination with a drug.